Re: [boost] New Borland compiler _MSC_VER mess [was: Boost ships with C++ Builder X]

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-11-28 10:39:39

Beman Dawes wrote:
> At 10:58 AM 11/27/2003, Peter Dimov wrote:
>> These contain
>>
>>    #if defined(_MSC_VER) && (_MSC_VER >= 1020)
>>    #  pragma once
>>    #endif
>>
>> which is intentional. As a general rule, compilers that expose _MSC_VER
do
>> support "#pragma once".
>
> That's why I made the point in the original posting about comments
> indicating intent. It would be a lot easier if the above had said
> something like:
>
>     #if defined(_MSC_VER) && (_MSC_VER >= 1020) // MS & compatible
> compilers
>     #  pragma once
>     #endif

OK, I've added a comment.

> or maybe:
>
>     BOOST_ONCE
>
> The BOOST_XXX macro approach seems preferable if it really is a
> commonplace usage (and thus something other compilers may add,
> perhaps with different spelling). Also would work well if Borland
> initially doesn't support #pragma once with their new compiler and
> then later does support it.

I'm not sure whether one can introduce a pragma with a macro, even if it
were possible, this requires a config.hpp dependency. #pragma once is only
used as an optimization in addition to the standard include guards. If I had
to include config.hpp I'd prefer to omit it entirely.

If Borland defines _MSC_VER but doesn't support #pragma once their users
will soon remind them that the Windows Platform SDK headers require it.